Serious accidents resulting in personal injury, maiming, and loss of life have occurred de to premature detonation of various explosive wireline tools such as perforating guns, casing or tubing cutters, string shot rods, jet cutters and the like. All such devices include powerful explosives that are extremely dangerous and which must be handled with great care. Even though great care is exercised, there still have been instances where premature firing has occurred after assembly of the tool onto the end of the cable, and before it has been inserted in the well. It is believed that such accidental firing can have many causes. For example, stray currents due to power leakage from defective wiring, generators, motors, electric welders and the like can be the cause. Other causes may be static charges produced by dust and electrical storms in the area, and by certain other atmospheric conditions. Ground currents produced by lightning, power lines, and galvanic action due to different soil strata can cause detonation. Some accidents have been thought to be due to operation of mobile, two-way communication equipment in the area.
There has been a continued and long-felt need for a safety device that will greatly reduce the possibility of accidental firing of the explosive due to causes such as those enumerated above. Injury to personnel most often occurs when the explosive goes off at the surface, either while rigging the tool up, or while the tool is being placed in the casing or tubing.
The general object of the present invention is to provide a new and improved bypass safety switch that will prevent premature firing of an explosive well tool.
Another object of the present invention is to provide a new and improved safety switch that functions to prevent flow of enough electric current to the detonator fuse of an explosive wireline tool to fire the same while the tool is being handled at the surface, and until it has been positioned well below the rig floor where service personnel might be present.